Thrust balancing



Dec. 15, 1964 L. B. SCHIBBYE THRUST BALANCING Filed Oct. 31, 1962 r- 2 Fig.1

34 0 L Fig.2 221V ATTORNEY United States Patent Ofitice 3,161,349 ?atented Dec. 15, 1964 3,161,349 THRUST BALANCENG Latrritz Benedictns Schibbye, Saltsjo-Duhnas, Sweden,

assignor to Svenslra Rotor Masiriner Alitieholag, Stochholm, Sweden, 2! company Filed (let. 31, HQ, S-ar. No. 234,436 Claims priority, application Sweden Nov. 8, 1961 8 Claims. (Cl. 230-143) The present invention relates to a particular kind of rotary piston, positive displacement machine for operation as a compressor or as an expander for elastic fluid. This kind of machine comprises a housing structure including a barrel portion comprised of intersecting bores with coplanar axes providing a working space extending longitudinally of the barrel portion and provided with end walls. port communicating with one end or" the working space, the major portion of which port is located at one side of the plane of the axes of the bores, and a high pressure port communicating with the other end of the working space, the major portion of which port is located at the opposite side of the said plane. This machine is provided with rotors with helical lands and grooves having an effective wrap angle of less than 360 which rotors are rotatably mounted in said bores and comprise male and female rotors. The male rotor has lands provided with substantially convexly curved flanks and intervening grooves the major portions of which lie outside the pitch circle of the male rotor. The female rotor has lands provided with substantially concavely curved flanks and intervening grooves the major portions of which lie inside the pitch circle of the female rotor. The lands and grooves of said rotors intermesh to form with the confronting portions of the housing structure chevron-shaped closed chambers. Each of the chambers is comprised of a portion of a male rotor groove and of a portion of a female rotor groove communicating therewith. Those chambers are defined at their base ends by an axially fixed transverse plane coinciding with the high pressure end wall of the working space and at their apex ends by the intermesh between the lands of the rotors. The apex ends move axially in relation to the fixed plane as the rotors revolve, whereby the volume of each chevronshaped chamber is varied. During this revolving one at a time of the chambers comes into communication with the high pressure port in a certain angular position of the rotors and the chambers have Zero volume with their apex ends lying in said fixed plane. The machine is further provided with means for supplying liquid to said working space for sealing the perimeters or" the chambers and cooling the contents thereof.

In machines of the actual kind, axial forces act on the rotors owing to the pressure difference between the high pressure and low pressure ports. Particularly a great axial force acts on the male rotor due to the formation of the lands. The axial forces necessitate on one hand means for fixing the rotors in relation to the housing structure on the other hand means for transmitting the forces from the rotors to the housing structure.

The means which fix the. rotors in relation to the housing structure shall have a minimum axial clearance for obtaining as good prformance as possible.

The space between the high pressure end wall of the Working space and the high pressure ends of the rotors forms in fact a channel between the portions of the grooves communicating with the high pressure and low pressure ports, respectively, so that too wide a space will cause considerable leakage losses. For this reason it is of very great importance that the space between the rotor ends and the end wall is kept as small as possible. The width of the space depends in the first place on the The housing structure has a low pressure clearance and elasticity of the thrust bearings. The type of the thrust bearings is thus of a very great importance. The space, however, must never decrease to zero, as a direct mechanical contact between the rotors and the end wall will cause a great risk for serious damages in the machine.

It is also for another reason of great importance that each thrust bearing is of such a type that its clearance and elasticity are small. This other reason being the risk that the diiferent rotors for a certain load will be put into different axial positions or into an axial oscillation, which means undesirable Variations in the peripheral, angularly controlled synchronization due to the helical lands. As the angular position between the rotors is usually determined by a special mechanical synchronizing gear there is thus a risk for seizing between the rotors which means that the clearance between the rotors must get a certain extent with regard to the undesirable variations in the synchronization deriving from the axial movements. As a small clearance between the rotors is desirable as regards the efficiency it is thus even for this reason important to choose the type of the thrust bearings for an axial displacement of the rotors which is small as possible.

As is evident from the above it is of the utmost significance for the function of the machine both with regard to the risk for mechanical damages and with regard to the efiiciency that an exact axial fixation is obtained. This requirement can not be fulfilled by using any kind of journal bearings as a bearing of this kind needs a relatively large clearance for obtaining a mechanical reliability. Furthermore the bearing losses in such a bearing increase considerably when the clearance decreases.

If on the other hand antifriction bearings are used a very small clearance or practically zero clearance may be obtained. Furthermore no increase of the bearing losses appears when decreasing the clearance as is the case for journal bearings.

An antifriction bearing, however, can not be so designed that it can carry as big a load as a journal bearing of the same dimensions and simultaneously obtain a requisite life. For this reason in machines of the actual type it has been unavoidable in many cases to use journal bearings as thrust bearings in spite of the disadvantages connected therewith owing to the increase of the bearing clearances and owing to the increase of the bearing losses.

Especially in machines with great pressure difference between the high pressure and low pressure ports it is important to decrease the axial forces acting on the bearings. Such machines can act either with a relatively high pressure on the low pressure side and a normal pressure ratio, i.e. a low pressure higher than the atmospheric pressure and a pressure ratio of 2:1 to 4:1, or with atmospheric presusre on the low pressure side and a high pressure ratio, for instance higher than 4:1. A typical example of the last kind of machines is a compressor with fluid injection and a pressure ratio of about 8:1. axial forces in machines of such a type are so large that if entirely carried, by thrust bearings of the antifriction type, roller or ball bearings, the bearings can not obtain a sulficient life owing to the fact that the available dimensions are limited by the pitch circles of the rotors, i.e. by the distance between the axes of the rotors. For that reason when carrying the whole axial force deriving from the working fluid by the bearings it is necessary to use journal bearings instead of antifriction bearings though the journal bearings as said above give considerably largeraxial' clearances and bearing losses than those of the antifriction bearings.

The object of the present invention is to eliminate the above mentioned difficulties as completely as possible.

The Y 7 3 According to the invention the problem will be solved by providing at least the shaft of the male rotor with balancing means which is intended to load the shaft with a force in opposite direction to the axial force deriving from the pressure of the working fluid. By suitable forming and sizing of this means an appropriate magnitudeof the oppositely directed force may be obtained so that anti-friclosses may be used as a thrust bearing. 7 Owing to the small axial force acting on the bearin the elasticity has been eliminated almost entirely. By forming the balancing device in such a way that the balancing force is a little larger than the maximum axial force deriving from the oneness working fluid the thrust bearing is continuously loaded controlling the pressure of the fluid and thus the balancing force. On the assumption that the liquid is com posed of lubricating oil the liquid leaking from the pres,- sure chamber can be used for lubrication of the adjacent bearings, whereby a special'supply of oil to these hearings may be avoided. In machines built for liquid injection the pressure chamber may suitably be so located in relation to the working space that the liquid leaking therebetween follows the shaft of the rotor to the space between the high pressure end wall of the working spaceand the high pressure end of the rotor in order to bring about an improved sealing of this space.

The special structural arrangement oi' the balancing means causes further advantages. Besides counterbal-v ancing of axial forces deriving from the working fluid there is also obtained a decrease of the size of the space between the high pressure end wall and the high pressure ends of the rotors. Pressure fluid leak owing to the difference between the pressure of the liquid and the pressure of the working fluid along the shaft of the rotor from the pressure chamber to the end .plane of the rotor. The outleaking liquid serves as a liquid seal against leakages of the Working fluid through the space. An improvement of the scaling is consequently obtained in this way owing to three separate factors which are, partlya decrease of the width of the spacebetween the high pressure end wall and the ends of the rotors due to the balancing piston, partly a liquid seal against leakage of the working fluid through the space in the transverse plane to the axes of the rotors, and partly a liquid seal against leakage of Working fluid along the shaft of the rotor from the Working space to the bearing casing. I l

The losses of power caused by such a rotatingpiston is very small due to the 'fact that there are large clearances between the rotating piston plate and the casing except the seals, which seals, however, have'got a small sealing area by forming them as labyrinth seals.

The invention will hereinafter be described more in detail with reference to an embodiment shown in the The compressor shown comprises a male rotor and a cooperating female rotor 12 having. helical, lands with intervening grooves. The major portions of the lands of the, male. rotor 10 lie outside the pitch circle of the round the stub shaft 2-6. the working space 2 9 by'a labryrinth seal 46 and from rotor and have substantially convexly curved flanks. The major portions of the lands of the female'rotor 12 lie inside the pitch circleo-fthe rotor and have substantially concavely curved flanks. The wrap angle of each land is less than 360 on each rotor. I

The'rotors It 12 are located in a housing structure provided with a barrel portion 14 and with end walls 16 and 18 enclosing a working space 20 substantially con.- prising two intersecting bores. The working space is provided with one low pressure port 22 and one high pressure port 24. The male rotor 10 is provided with a stub shaft 26 which projects outside the end wall 16 and which is adapted for connection with a driving motor, not shown. The male rotor is furthermore mou'nted in the/end Wall 18 by a roller bearing 28 and in the end Wall 16, by a roller hearing 33 and a ball bearing 32. The roller bearings 23 and 30 carry only radial forces. and the ball hearing 32 carries the axial force. v

The compressor is further provided with an inlet 34 to a space 35 for high pressure liquid. The liquid is injected from the space 36 to theworking space 2t through a number of slots 38 provided along the line of intersection between the bores of the working space.

In the end Wall 16 is further provided an inlet for high pressure oil to an annular-shaped space 44 provided The space 44 is separated from the bearing casing 56 by an annular piston 43 which is pressed in axial 'direction'against the inner ring of the ball bearing 32. v

A compressor of this kind with liquid injection may, as known per so, be used for high pressure ratios due to the cooling and sealing qualities of the liquid. Consequently there are large axial forces deriving from the Working fluid and acting on the rotors, particularly the male rotor It). By supplying the compressor with pressure liquid not only to th spaceSfi for injecting oil into the working space 20 but also to the space 44, the balancing piston 48 will be loaded with an axial forcefrom the pressure liquid which force acts in opposite direction to the force that acts upon the rotor deriving from the working fluid. Because of the labyrinth seal 46 against the working space 2% the leakage to the space 20 will be restricted and the pressure in the space 44 be fixed, which in combination with suitable dimensions ofthe area of the piston gives a possibility to lit the axial force deriving from the liquid so that the axial forces acting on the inner ring of the ball bearingbalance each other as close as possible. In this Way theaxial force of the'rotor will be balanced before it has acted on the thrust bearing of the rotor, whereby an" antifriction bearing serving as a thrust hearing may'ob-tain a satisfying life which causes that the good qualities of this bearing with reference to friction losses'and the size of the axial clearance fully may be made use of in spite of the large axial force deriving from the working fluid. 3 j

The invention is ofv'course not limited to the shown embodiments but includes everything lying within the scope of the, accompanying claims. It may particularly be pointed out although it has not been shown that it is obvious that balancing means of the shown kind also may be applied to expanders; Iclaimz I l. A rotary piston, positive displacement, elastic fluid machine having a housing structure including a barrel portion-comprised of intersecting bores with 'co-planar axes" providing a working space extending longitudinally Y of saidbarrel portion and provided with a high pressure end wall, said structure having a low pressure port com- I municating with one end of said space the major portion an effective wrap angle of less than 360 rotatably mounted in said bores and comprising a male rotor having lands provided with substantially convexly curved flanks and intervening grooves the major portions of which are outside the pitch circle of the male rotor and a female rotor having lands provided with substantially concavely curved flanks and intervening grooves the major portions of which lie inside the pitch circle of the female rotor, the lands and grooves of said rotors intermeshing to form with the confronting portions of said housing structure chevron-shaped closed chambers each comprised of a portion of a male rotor groove and of a portion of a female rotor groove communicating therewith, said chambers being defined at their base ends by said high pressure end Wall of the working space and at their apex ends by the places of intermesh between the lands of the rotors, said apex ends moving axially toward said high pressure end wall as the rotors revolve to decrease the volume of said chambers and said chambers coming into communication serially with said high pressure port, means for supplying liquid to said working space for sealing the perimeters of said chambers and cooling the contents thereof, said male rotor having a shaft part extending through said high pressure end wall and said housing structure forming a pressure chamber encircling said shaft part on the side of said high pressure end Wall remote from the body portion of said male rotor, sealing means between said shaft part and said high pressure end wall, a balancing piston in said pressure chamber fixed in sealing engagement with said shaft part against axial displacement thereon in a direction away from said high pressure end wall, and means for supplying liquid under pressure to said pressure chamber between said balancing piston and said high pressure end wall to produce an axial thrust on said male rotor acting in opposition to the axial thrust exerted thereon by the fluid being compressed in said compression chambers.

2. A machine as defined in claim 1 in which the same kind of liquid is supplied both to said working space and to said pressure chamber.

3. A machine as defined in claim 2 in which said liquid is lubricating oil.

4. A machine as defined in claim 3 in which the sealing means between said shaft part and said high pressure end wall is of the labyrinth type permitting limited leakage of oil from said high pressure chamber to said working space between the high pressure end faces of said rotors and the confronting face of the high pressure end wall, whereby to minimize leakage of high pressure compressed elastic fluid in the working space across said end faces from the high pressure side of the machine to the low pressure side of the machine.

5. A machine as defined in claim 1 in which said piston is fixed to rotate with said shaft part of the male rotor and a labyrinth type seal is provided between the perimeter of said piston and the Wall of said chamber to provide a minimum of frictional loss due to the rotating piston.

6. A machine as defined in claim 1 in which said shaft part on the side thereof remote from said piston is carried by anti-friction bearing means mounted in said housing structure.

7. A machine as defined in claim 6 in which said hearing means comprises separate bearings for carrying the radial and the axial thrust loads on said shaft parts and in which the bearing for carrying said thrust load is a ball bearing.

8. A machine as defined in claim 6 in which the liquid supplied to said pressure chamber is lubricating oil, and said balancing piston is mounted to rotate with said shaft part and is provided at its perimeter with a labyrinth seal permitting leakage flow of oil past the seal to lubricate said bearing means.

References titted in the file of this patent UNITED STATES PATENTS 681,581 Richards Aug. 27, 1901 1,634,023 Davison June 28, 1927 1,673,260 Meston et al June 12, 1928 1,675,524 Zajac July 3, 1928 1,677,980 Montelius July 24, 1928 1,698,802 Montelius Jan. 15, 1929 2,095,168 Burghauser Oct. 5, 1937 2,174,522 Lysholm Oct. 3, 1939 2,287,716 Whitfield June 23, 1942 2,622,787 Nilsson Dec. 23, 1952 FOREIGN PATENTS 903,500 Germany Feb. 8, 1954 541,601 Great Britain Dec. 3, 1941 

1. A ROTARY PISTON, POSITIVE DISPLACEMENT, ELASTIC FLUID MACHINE HAVING A HOUSING STRUCTURE INCLUDING A BARREL PORTION COMPRISED OF INTERSECTING BORES WITH CO-PLANAR AXES PROVIDING A WORKING SPACE EXTENDING LONGITUDINALLY OF SAID BARREL PORTION AND PROVIDED WITH A HIGH PRESSURE END WALL, SAID STRUCTURE HAVING A LOW PRESSURE PORT COMMUNICATING WITH ONE END OF SAID SPACE THE MAJOR PORTION OF WHICH PORT IS LOCATED AT ONE SIDE OF THE PLANE OF SAID AXES AND A HIGH PRESSURE PORT COMMUNICATING WITH THE OTHER AND HIGH PRESSURE END OF SAID SPACE THE MAJOR PORTION OF WHICH PORT IS LOCATED AT THE OPPOSITE SIDE OF SAID PLANE, ROTORS PROVIDED WITH HELICAL LANDS AND GROOVES HAVING AN EFFECTIVE WRAP ANGLE OF LESS THAN 360* ROTATABLY MOUNTED IN SAID BORES AND COMPRISING A MALE ROTOR HAVING LANDS PROVIDED WITH SUBSTANTIALLY CONVEXLY CURVED FLANKS AND INTERVENING GROOVES THE MAJOR PORTIONS OF WHICH ARE OUTSIDE THE PITCH CIRCLE OF THE MALE ROTOR AND A FEMALE ROTOR HAVING LANDS PROVIDED WITH SUBSTANTIALLY CONCAVELY CURVED FLANKS AND INTERVENING GROOVES THE MAJOR PORTIONS OF WHICH LIE INSIDE THE PITCH CIRCLE OF THE FEMALE ROTOR, THE LANDS AND GROOVES OF SAID ROTORS INTERMESHING TO FORM WITH THE CONFRONTING PORTIONS OF SAID HOUSING STRUCTURE CHEVRON-SHAPED CLOSED CHAMBERS EACH COMPRISED OF A PORTION OF A MALE ROTOR GROOVE AND OF A PORTION OF A FEMALE ROTOR GROOVE COMMUNICATING THEREWITH, SAID CHAMBERS BEING DEFINED AT THEIR BASE ENDS BY SAID HIGH PRESSURE END WALL OF THE WORKING SPACE AND AT THEIR APEX ENDS BY THE PLACES OF INTERMESH BETWEEN THE LANDS OF THE ROTORS, SAID APEX ENDS MOVING AXIALLY TOWARD SAID HIGH PRESSURE END WALL AS THE ROTORS REVOLVE TO DECREASE THE VOLUME OF SAID CHAMBERS AND SAID CHAMBERS COMING INTO COMMUNICATION SERIALLY WITH SAID HIGH PRESSURE PORT, MEANS FOR SUPPLYING LIQUID TO SAID WORKING SPACE FOR SEALING THE PERIMETERS OF SAID CHAMBERS AND COOLING THE CONTENTS THEREOF, SAID MALE ROTOR HAVING A SHAFT PART EXTENDING THROUGH SAID HIGH PRESSURE END WALL AND SAID HOUSING STRUCTURE FORMING A PRESSURE CHAMBER ENCIRCLING SAID SHAFT PART ON THE SIDE OF SAID HIGH PRESSURE END WALL REMOTE FROM THE BODY PORTION OF SAID MALE ROTOR, SEALING MEANS BETWEEN SAID SHAFT PART AND HIGH PRESSURE END WALL, A BALANCING PISTON IN SAID PRESSURE CHAMBER FIXED IN SEALING ENGAGEMENT WITH SAID SHAFT PART AGAINST AXIAL DISPLACEMENT THEREON IN A DIRECTION AWAY FROM SAID HIGH PRESSURE END WALL, AND MEANS FOR SUPPLYING LIQUID UNDER PRESSURE TO SAID PRESSURE CHAMBER BETWEEN SAID BALANCING PISTON AND SAID HIGH PRESSURE END WALL TO PRODUCE AN AXIAL THRUST ON SAID MALE ROTOR ACTING IN OPPOSITION TO THE AXIAL THRUST EXERTED THEREON BY THE FLUID BEING COMPRESSED IN SAID COMPRESSION CHAMBERS. 